Infant colic or prolonged, inconsolable crying in an otherwise healthy infant has been a source of confusion for parents and pediatricians alike. Much of this is due to the lack of concrete evidence as to its origins. Adding to the confusion is the finding that colic may have an impact on later infant behavior or parent perceptions of that behavior. The purpose of the proposed research is to address these issues by investigating the physiological and behavioral antecedents and correlates of infant colic and to examine its influences on later infant development. Toward these ends, two studies are proposed. One is a longitudinal study designed to prospectively identify and follow a group of colic and non-colic infants from birth to ten months of age. Two other groups, one an irritable group that cries frequently but does not meet colic criteria, and one that exhibits excessive gastrointestinal symptoms but not excessive crying will also be followed. The emergence of colic will be identified at its onset and behaviors associated with colic obtained through the use of diaries. Anecdotal reports and our preliminary study of behaviors exhibited during a colic bout suggest that infants are expressing gastrointestinal pain. Work with adults using the non-invasive electrogastrogram (EGG) has shown reports of gastrointestinal upset to be associated with dysrhythmia. We propose to record the EGGs of colic infants during a baseline and colic condition to determine whether changes in normal rhythms are associated with colic cry behavior. To determine the contribution of infant temperament to the emergence of colic and whether colic influences infant behavior once it has dissipated, we propose to measure infant reactivity and regulation at birth, five months, and 10 months of age through laboratory procedures and parental ratings. A second cross-sectional study is proposed to examine the development of gastric myoelectric activity within the first year of life using the EGG. To date, no developmental studies using this measure exist. This study will precede the longitudinal study as the results are essential to our understanding of the physiological changes associated with colic. Both studies will contribute important information to several areas of infant health and development.